1. Field of the Invention
The present invention pertains to inspection devices, and more particularly, to inspection devices that are used for contact lenses.
2. Description of the Prior Art
Currently available inspection devices employ image-capturing technology. There are many types of image-capturing devices within the prior art. The size of the apertures used on these prior art devices can range from small apertures to large apertures. It is well known within the imaging arts that a greater depth of field results from using a smaller aperture. Examples of imaging devices that use small apertures are single-use cameras and WebCams. Small apertures are very useful in providing simultaneous focus of objects from three feet to infinity. A shortcoming in the application of small apertures is that only a small amount of light can pass through the small aperture. Imaging devices having small apertures typically require brighter light as compared to similar imaging devices having larger apertures. Those imaging devices that have large apertures inherently allow greater amounts of light to pass through the larger apertures but suffer in that they have a smaller depth of field than the devices that employ smaller apertures.
Inspection systems for optical devices that currently exist typically use large apertures in their optics to create essentially two-dimensional inspection systems. In these two-dimensional systems, a wide-open lens allows substantial amounts of light to pass through, resulting in a bright, consistently-illuminated image that is displayed on a screen. A shortcoming within the prior art devices employing a large aperture lens is that they have a very shallow depth of field.
Currently available inspection devices for contact lenses are essentially two-dimensional systems. Typically, the light source is no more than a halogen light bulb that is used without any reflector at all. These prior art inspection devices do not employ a reflector because sufficient light is available in these systems. Large apertures on an objective lens allow much light to pass, resulting in a bright image but little depth of field. A glass stage is commonly used to retain the object being inspected. The light beam shines through the glass of the stage and backlights the object being inspected. The shadow created by the object is focused through the objective lens and projected very accurately on a screen in front of an inspector who may observe, inspect or take measurements of the edges of the shadow of the object. These two-dimensional inspection devices can also be used to inspect transparent materials for defects. Since the two-dimensional inspection devices are designed to measure the shadow of the object accurately, they have a very narrow depth of field. The result is that only surfaces that are in a flat plane parallel to the objective lens will be in focus. Surfaces at differing heights will not be in focus at the same time. Adjustments can be made to the position of the glass stage retaining the object that is being inspected allowing different portions of the object to be in focus and enabling different features of the object to be inspected.